Development of Trichogramma australicum Girault (Hymenoptera: Trichogrammatidae) on Helicoverpa armigera (Hübner) Eggs (Lepidoptera: Noctuidae)

Abstract

Trichogramma australicum were reared on eggs of Helicoverpa armigera. Immature T. australicum were studied with a confocal laser scanning microscope and a light microscope. Development of egg, larva, prepupa and pupa required about 24-26, 24-26, 42-47 and 84-92 h, respectively, at 28°C, 45% RH and 12L:12D photoperiod. The eggs of T. australicum increased significantly in size during incubation. The larval mandibles were gradually revealed as the larva increased in size. Exuviae were not found during the larval stage, and we conclude that T. australicum has one larval instar. Staining larvae and pre-pupae with 1% aniline blue dissolved in Neisenheimer's solution induced fluorescence. Stained larvae and pre-pupae gave a clear image of anatomy when observed with a confocal laser scanning microscope. Urate bodies appeared at the onset of the prepupal stage. The vitelline membrane of host egg gradually blackened. Legs, wings, antennae, body segmentation, genitalia, colour of compound eyes and ocelli became distinct during the prepupal stage. Larval integument and mandibles were shed at the onset of pupation. The adult wasps emerged 182.40 ± 0.40 h (n = 10) after oviposition, 2.80 ± 0.25 (n = 10) wasps emerged from a host egg, and the sex ratio was 1 ♂ :3 ♀♀.